Fabrication of conventional semiconductor structures requires forming aligned features within the semiconductor structure. Frequently, photolithography or other lithographic techniques are used to form the aligned features within the semiconductor structure. However, as the number of patterning and photolithography acts increases, the processing time and cost of fabricating the semiconductor structure, as well as the potential for contamination and structural defects, increases. Accordingly, reducing the number of patterning steps is often a goal of semiconductor fabrication methods.
It may be desired to form aluminum oxide at select locations of a semiconductor structure. FIG. 1A illustrates a semiconductor structure 100 at an intermediate processing stage. Aluminum oxide 116 may be formed over a substrate 110 including isolation regions 112. While the aluminum oxide 116 is only desired at a specific location (see FIG. 1C), the aluminum oxide 116 is initially formed over the entire substrate 110 and portions subsequently removed. Additional semiconductor materials 114 may be formed between the aluminum oxide 116 and the substrate 110. A bottom anti-reflective coating (BARC) 140 and a photoresist 150 may be formed over the aluminum oxide 116. Referring to FIG. 1B, portions of the photoresist 150 and the BARC 140 may be removed to produce a desired pattern, which is transferred to the aluminum oxide 116. Referring to FIG. 1C, the aluminum oxide 116 may be removed through the patterned photoresist 150 and BARC 140. However, removing the aluminum oxide 116 may result in undesired damage to exposed materials of the semiconductor structure 100. For example, etching aluminum oxide 116 often requires aggressive etch chemistries that may damage materials of the semiconductor structure 100, such as a dielectric material or a gate oxide. As an example, aluminum oxide may be removed by etching with a solution of ammonium hydroxide, hydrogen peroxide, and water. The ammonium hydroxide and hydrogen peroxide may have concentrations up to about thirty weight percent (30 wt. %). Aluminum oxide may also be removed with etchants such as Br2 in a methanol solution, or with etchants including strong acids such as HF, HCl, phosphoric acid, sulfuric acid, and combinations thereof. The etch chemistries may also undercut the aluminum oxide 116 in regions where the aluminum oxide 116 is desired. Because of the aggressive nature of such etchants, it may be difficult to control the thickness of the aluminum oxide and to prevent damage to materials of the semiconductor structure 100, such as materials underlying the aluminum oxide. Thus, forming aluminum oxide in desired locations on a semiconductor structure is a challenge.
Therefore, it would be desirable to have a method of forming a self-aligned aluminum oxide material without damaging the materials proximate to the aluminum oxide or undercutting the aluminum oxide. It would also be desirable to be able to form a self-aligned aluminum oxide material that does not require etching aluminum oxide and does not require a wet BARC and photoresist material.